: The goal of this project is to develop therapeutic applications for leptin in treatment of hematopoietic diseases and transplantation. Recently they have found that leptin affects the survival and expansion of a population of bone marrow cells. A thorough characterization of the effect of leptin on fractionated bone marrow cells will be performed. The lineage of leptin specific target cells will be further delineated and the functional role of leptin in hematopoiesis will be investigated. Information obtained from this Phase 1 research will indicate the feasability of utilizing leptin as a therpeutic agent for the ex vivo expansion of trasnplantable progenitor cells and in vivo to accelerate recovery after transplantation.